Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, composite, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
III-nitride devices are often grown on sapphire or SiC substrates. In conventional devices, an n-type GaN region is grown on the substrate, followed by an InGaN active region, followed by an AlGaN or GaN p-type region. The difference in lattice constant between the non-III-nitride substrate and the III-nitride layers, as well as the difference in lattice constant between III-nitride layers of different composition, causes strain in the device. The strain energy due to lattice mismatch can cause defects and decomposition of the InGaN active region, which may cause poor device performance. Since the strain energy is a function of both the composition of the InGaN light emitting layer (which determines the amount of strain) and the thickness of the light emitting layer, both the thickness and composition are limited in conventional III-nitride devices.
Ougazzaden et al. Bandgap bowing in BGaN thin films, Applied Physics Letters 93, 083118 (2008) reports on “thin films of BxGa1-xN grown on AlN/sapphire substrates using metal-organic vapor phase epitaxy.” See, for example, Abstract. “Ternary and quaternary layers of nitrides are important for bandgap engineering of GaN-based optoelectronic devices. The introduction of boron, which is a ‘light’ element, could, in principle, compensate for the strain induced by a high fraction of ‘heavy’ indium in InGaN-based light emitters and could provide lattice matching for BGaN grown on AlN and SiC substrates.” See, for example, the first paragraph in the first column on the first page of Ougazzaden et al.